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Injection dykes as evidence of Campanian synsedimentary tectonics on the Kraków Swell, southern Poland

Keywords: injections dykes , synsedimentary tectonics , biostratigraphy , Late Cretaceous , Campanian , Kraków Swell , Poland

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Abstract:

The topmost part of the Oxfordian limestones, building the Zakrzówek Horst in Kraków, is featured by a network of minute fissures, filled with Upper Cretaceous limestones. Fissures are dominantly subhorizontal, anastomosing and polygonal in plane. They are filled with white limestones representing mostly foraminiferal- calcisphere wackestones, with subordinate amount of quartz pebbles and fragments of stromatolite coming from the latest Turonian-?Early Coniacian conglomerate overlying Oxfordian basement. The fissures are seismically- induced injection dykes. In contrast to gravitationally-filled neptunian dykes the recognised injection dykes were filled by overpressured soft sediments. Foraminifera within some dykes are abundant, and dominated by plankto- nic forms, which indicate the Early/Late Campanian age (Globotruncana ventricosa and Globotruncanita calcarata zones) of the filling, and hence date also the synsedimentary tectonics. Abundant and diversified keeled globo- truncanids in the Campanian of the Kraków region are recognised for the first time. Other important findings at the studied section include karstic cavities featuring the surface of the Oxfordian bedrock filled with conglomerates of the latest Turonian-?Early Coniacian age based on foraminifera and nannoplankton, and lack of Santonian deposits, which elsewhere are common in the Upper Cretaceous sequences in the Kraków region. The discovered Campanian dykes provide new evidence for the Late Cretaceous tectonic activity on the Kraków Swell related to the Subhercynian tectonism, which resulted among others in stratigraphic hiatuses and unconformities characte- ristic of the Turonian-Santonian interval of this area.

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